Host cells and culture methods

ABSTRACT

Improved host cells and culture methods involving overexpression of MAN1C1 activity to improve protein production are provided.

The present application claims benefit under 35 U.S.C. § 119 of U.S.patent application Ser. No. 60/749,076, which was filed Dec. 8, 2005,and is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to improved host cells and culture methods thatimprove glycoprotein production.

BACKGROUND OF THE INVENTION

Methods of increasing recombinant host protein production in thepharmaceutical industry and in the laboratory are highly desirable inmany ways, including cost savings, times savings, and manufacturingcapacity. Treatment with sodium butyrate has been one means ofincreasing protein production in cell culture in commercialbiopharmaceutical processes. However, the derived benefit of increasedprotein yields is sometimes offset by the toxic side effects of sodiumbutyrate.

Sodium butyrate is a short chain fatty acid that inhibits the histonedeacetylase (HDAC) enzyme responsible for the maintenance of chromatinstructure in the nucleus of cells (Davie, J. Nutrition 133: 2485S-2493S,2003). The loss of activity results in an alteration in transcriptionalregulation of genes through the normal acetylation and deacetylationprocess of histones (Prasad et al., In Vitro 12: 125-132, 1976). Thechange in transcriptional regulation has been shown to increase thespecific productivity of cell lines producing recombinant proteins invitro. For example, sodium butyrate has been shown to increase thesynthesis of secreted recombinant follicle stimulating hormone (FSH),tissue plasminogen activator (tPA), erythropoietin (EPO), andthrombopoietin (TPO) in Chinese hamster ovary (CHO) cells (Sung et al.,J. Biotechnology 112: 323-335, 2004; Hendrick et al. Cytotechnology 36:71-83, 2001; Chung et al., J. Microbiol. Biotechnol. 11, 1087-1092,2001; Chotigeat et al., Cytotechnology 15: 217-221, 1994; Chang et al.,Free Radical Research 30: 85-91, 1999). The precise mechanismsresponsible for these increases are uncertain. Sodium butyrate treatmenthas been shown to transiently increase mRNA levels for recombinantprotein, resulting in increases in resulting protein biosynthesis (Yuanet al., J. Biol. Chem. 260: 3778-3783, 1985).

Changes in gene expression caused by sodium butyrate have been studiedpreviously in cell lines involved in colon cancer research. The studiesdemonstrated that sodium butyrate alters the expression of multiplegenes involved in cell cycle progression, differentiation, cytokinesignaling, and apoptosis. However, such studies were limited torelatively a small subset of genes and did not determine whether geneswere involved in protein biosynthesis. (Joseph et al., Oncogene 23:6304-6315, 2004; Tabuchi et al., Biochem. Biophys. Research Comm. 293:1287-1294, 2002; Iacomino et al., Biochem. Biophys. Research Comm. 285:1280-1289, 2001; Mariadason et al., Cancer Res. 60: 4561-4572, 2000;Della Ragione et al., FEBS Letters 499, 199-204, 2001).

Alpha 1,2 mannosidase I enzyme (MAN1C1) is an enzyme involved inglycoprotein N-linked oligosaccharide processing that has been describedin Tremblay et al. (Glycobiology 8: 585-595, 1998) and Gonzalez et al.(J. Biol. Chem. 274: 21375-21386, 1999). The enzyme catalyzes the firstmannose trimming step associated with processing of high mannoseoligosaccharide structures by removing a terminal mannose sugar from theoligosaccharide. N-terminal glycosylation involves the addition andremoval of various monosaccharide sugars in both the endoplasmicreticulum (ER) and Golgi compartments (Komfeld et al., Ann. Rev.Biochem. 54: 631-664, 1985). In the ER, the N-linked glycosylation isaccompanied by the folding of nascent glycoproteins into their nativestructure through interactions with molecular chaperones (Ellgaard etal., Science 286: 1882-1888, 1999; Jakob et al., J. Cell Biol. 142:1223-1233, 1998). This process has been termed ER quality control, andif the process is blocked due to a misfolded protein, the onset of ERassociated degradation, or ERAD, of the protein typically occurs(Ellgaard et al., Curr. Opin. Cell Biol. 13: 431-437, 2001; Sifers,Science 299: 1330-1331, 2003; Oda et al., Science 299: 1394-1397, 2003;Molinari et al., Science 299:1397-1400, 2003; Hurtley et al., Ann. Rev.Cell Biol. 5: 277-307, 1989). The removal of a terminal mannose sugarfrom Man₉ to Man₈ by the alpha 1,2 mannosidase I enzyme (MAN1C1) hasbeen shown to affect the onset of the ERAD response (Liu et al., J.Biol. Chem. 274: 5861-5867, 1999; Grinna et al. J. Biol. Chem. 255,2255-2258, 1980).

In view of the toxicity of protein production inducers such as sodiumbutyrate, there exists a need for other means of increasing overallproduction of recombinant proteins in cell culture.

SUMMARY OF THE INVENTION

The present invention provides host cells engineered to overexpressalpha 1,2 mannosidase (MAN1C1) and a glycoprotein or protein ofinterest. Such host cells may comprise a heterologous expression controlsequence operably linked to a nucleic acid encoding MAN1C1, and aheterologous expression control sequence operably linked to a nucleicacid encoding such glycoprotein. The host cells may engineered tooverexpress either or both MAN1C1 and the glycoprotein of interest byany means known in the art, including transfection with a vectorcomprising a nucleic acid encoding the protein, wherein the nucleic acidis operably linked to a heterologous expression control sequence, ortransfection with an expression control sequence that upregulatesexpression of endogenous protein.

The invention further provides methods of producing a glycoprotein ofinterest comprising the steps of: culturing any of the host cells of theinvention in culture medium; and recovering such glycoprotein from thehost cell or culture medium. Such a host cell is cultured underconditions that induce increased MAN1C1 protein expression or increasedspecific productivity of the glycoprotein of interest. It is furthercontemplated that such a host cell expresses MAN1C1 protein at a levelthat increases the amount (pg/mg protein) or specific productivity(pg/cell/day) of such glycoprotein produced. Improvements in suchglycoprotein production or specific productivity may be, e.g., at least2-fold, 3-, 4-, 5-, 6-, 7-, 8-, 9-, 10-, 15-, or 20-fold or higher.

The invention also contemplates methods of increasing production of aglycoprotein of interest comprising the step of further adding aninducer of protein production to the culture medium. Inducers of proteinproduction are well known to one of skill in the art and are furtherprovided herein.

The host cells and methods of the invention may be used to produce anyglycoprotein or protein of interest. Exemplary glycoproteins includeerythropoiesis-stimulating molecules such as erythropoietin ordarbepoetin, or analogs, variants, or derivatives thereof. Host cells ofthe invention may be, but are not limited to, mammalian cells, CHOcells, human cells, BHK cells, NS/0 cells, HT-1080 cells, or any othercell known to be useful in one of skill in the art.

In another aspect, the invention provides methods of screening for aninducer of protein production comprising the steps of: contacting a hostcell with a candidate compound, determining expression level of MAN1C1,and identifying said candidate compound as an inducer of proteinproduction if the expression level of MAN1C1 increases. Such a methodcontemplates determining mRNA expression levels or protein expressionlevels.

Other features and advantages of the invention will become apparent fromthe following detailed description. It should be understood, however,that the detailed description and the specific examples, whileindicating exemplary embodiments of the invention, are given by way ofillustration only, because various changes and modifications within thespirit and scope of the invention will become apparent to those skilledin the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 displays measured rHuEPO specific productivity (Q_(P)) over 5-dayculture in the presence of sodium butyrate.

FIG. 2A shows the effect of MAN1C1 siRNA treatment on rHuEPO Q_(P) inthe presence of sodium butyrate over a 5-day period. FIG. 2B displaysthe fold change in MAN1C1 mRNA levels in HT1080 cells treated withsodium butyrate or sodium butyrate plus siRNA.

FIG. 3 displays changes in rHuEPO mRNA levels in HT1080 cells treatedwith sodium butyrate in the presence and absence of siRNA directedagainst MAN1C1.

FIG. 4 displays changes in rHuEPO specific productivity after transienttransfection with varying amounts of MAN1C1 DNA.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides materials and methods for increasing therecombinant production of a protein of interest in host cells. As usedherein, a “protein of interest” is a protein (other than MAN1C1) forwhich the recombinant production of bulk quantities of such protein isdesired.

More specifically, the invention includes host cells producing arecombinant protein of interest that have been additionally engineeredto overexpress alpha 1,2 mannosidase I enzyme (MAN1C1), cell culturescontaining such host cells, and methods of producing increased amountsof the recombinant protein of interest comprising culturing such hostcells under conditions such that MAN1C1 is expressed at levels higherthan normal. The expression of higher levels of MAN1C1 results inimprovements in specific productivity and/or protein production of theprotein of interest.

The invention also contemplates methods of improving protein productionor increasing specific productivity involving increasing the levels ofMAN1C1 activity in host cells through introduction of chemical inducersthat increase MAN1C1 protein production, or chemical inducers thatincrease the specific activity of MAN1C1 expressed.

The invention contemplates methods wherein the improved specificproductivity measures at least 2 pg glycoprotein/cell/day. In exemplaryembodiments, the specific productivity measures at least 3, 4, 5, 6, 7,8, 9, 10, 11, 12, 13, 14, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80,90, or 100 pg glycoprotein/cell/day. However, greater specificproductivity is contemplated, especially with the use of additionalinducers.

The present invention determined that one mechanism by which sodiumbutyrate increases protein production is through upregulating expressionof MAN1C1, a gene involved in glycosylation of proteins. The datadescribed herein show that high levels of MAN1C1 expression do notsignificantly alter glycosylation of glycoproteins but unexpectedlyincrease the amount of recombinant protein produced. MAN1C1 mRNAexpression was shown to dramatically increase when cells were treatedwith sodium butyrate, to roughly 10-fold higher over a 24 hour periodand greater than 40-fold over five day period. Treatment of host cellsexpressing a recombinant protein of interest with siRNA to reduce MAN1C1protein expression reduced by 50% the sodium butyrate-induced increasein production of the protein of interest. Moreover, overexpression ofMAN1C1 in the absence of sodium butyrate resulted in a 2-3 fold increasein production of the protein of interest. Thus, the increased expressionof MAN1C1 contributes to the increase in specific productivity of theprotein of interest.

The term “isolated nucleic acid” refers to a nucleic acid of theinvention that is free from at least one contaminating nucleic acid withwhich it is naturally associated. A “nucleic acid” refers to a DNA orRNA sequence, optionally including artificial bases or base analogs.

The term “identity” (or “percent identical”) is a measure of the percentof identical matches between the smaller of two or more sequences withgap alignments (if any) addressed by a particular mathematical model orcomputer program (i.e., “algorithms”). The term “similarity” is arelated concept but, in contrast to “identity”, includes both identicalmatches and conservative substitution matches. Identity and similarityof related nucleic acid molecules and polypeptides can be readilycalculated by known methods. Preferred methods is to determine identityand/or similarity are designed to give the largest match between thesequences tested. Methods to determine identity and similarity aredescribed in publicly available computer programs. Exemplary computerprogram methods to determine identity and similarity between twosequences include, but are not limited to, the GCG program package,including GAP (Devereux et al., Nucl. Acids. Res. 12: 387, 1984;Genetics Computer Group, University of Wisconsin, Madison, Wis.),BLASTP, BLASTN, and FASTA (Altschul et al., J. Mol. Biol. 215:403-410,1990)). The BLASTX program is publicly available from the NationalCenter for Biotechnology Information (NCBI) and other sources (BLASTManual, Altschul et al. NCB/NLM/NIH Bethesda, Md. 20894; Altschul etal., supra). The well-known Smith-Waterman algorithm may also be used todetermine identity. Preferred parameters for a polypeptide sequencecomparison include the following: Algorithm: Needleman et al., J. Mol.Biol. 48: 443-453, 1970; Comparison matrix: BLOSUM 62 from Henikoff etal., Proc. Natl. Acad. Sci. USA 89: 10915-10919, 1992); Gap Penalty: 12,Gap Length Penalty: 4; Threshold of Similarity: 0. The GAP program isuseful with the above parameters (along with no penalty for end gaps).Preferred parameters for nucleic acid molecule sequence comparisonsinclude the following: Algorithm: Needleman et al., J. Mol. Biol., 48:443-453, 1970; Comparison matrix: matches=+10, mismatch=0, Gap Penalty:50, Gap Length Penalty: 3. The GAP program is also useful with the aboveparameters. Other exemplary algorithms, gap opening penalties, gapextension penalties, comparison matrices, thresholds of similarity, etc.may be used by those of skill in the art.

The term “operably linked” refers to a functional linkage between anexpression control sequence and a second nucleic acid sequence, whereinthe expression control sequence directs transcription of the nucleicacid corresponding to the second sequence.

The phrase “stringent hybridization conditions” refers to conditionsunder which a probe will hybridize to its target subsequence, typicallyin a complex mixture of nucleic acid, but to no other sequences.Hybridization stringency is principally determined by temperature, ionicstrength, and the concentration of denaturing agents such as formamide.Examples of “highly stringent conditions” for hybridization and washingare 0.015M sodium chloride, 0.0015M sodium citrate at 65-68° C. or0.015M sodium chloride, 0.0015M sodium citrate, and 50% formamide at 42°C. See Sambrook, Fritsch & Maniatis, Molecular Cloning: A LaboratoryManual, 2nd Ed., Cold Spring Harbor Laboratory, (Cold Spring Harbor,N.Y. 1989); (1989) and Anderson et al., Nucleic Acid Hybridisation:Hybridization: a practical approach, Ch. 4, IRL Press Limited (Oxford,England). Limited, Oxford, England (1999). Examples of typical“moderately stringent” conditions are 0.015M sodium chloride, 0.0015Msodium citrate at 50-65° C. or 0.015M sodium chloride, 0.0015M sodiumcitrate, and 20% formamide at 37-50° C. By way of example, a “moderatelystringent” condition of 50° C. in 0.015 M sodium ion will allow about a21% mismatch.

It will be appreciated by those skilled in the art that there is noabsolute distinction between “highly” and “moderately” stringentconditions. For example, at 0.015M sodium ion (no formamide), themelting temperature of perfectly matched long DNA is about 71° C. With awash at 65° C. (at the same ionic strength), this would allow forapproximately a 6% mismatch. To capture more distantly relatedsequences, one skilled in the art can simply lower the temperature orraise the ionic strength.

The term “vector” is used to refer to any molecule (e.g., nucleic acid,plasmid, or virus) used to transfer coding information to a host cell.

The term “expression vector” refers to a vector which is suitable foruse in a host cell and contains nucleic acid sequences which directand/or control the expression of desired nucleic acid sequences(“expression control sequences”). Suitable expression control sequencesinclude constitutive or inducible or regulatable promoters, enhancers oran array of transcription factor binding sites. “Expression” includes,but is not limited to, processes leading to protein production such astranscription, translation, and RNA splicing, if introns are present.

A “heterologous” expression control sequence operably linked to anucleic acid refers to an expression control sequence that is operablylinked to a nucleic acid (including a gene) that is different from thegene to which the expression control sequence is normally operablylinked in its native state.

The term “host cell” is used to refer to a cell which has beentransformed, or is capable of being transformed with a nucleic acidsequence and then of expressing a selected gene of interest. The termincludes the progeny of the parent cell, whether or not the progeny isidentical in morphology or in genetic make-up to the original parent, solong as the selected gene is present.

As used herein, a host cell “engineered to overexpress” a protein (or anucleic acid encoding such protein) is a host cell, including adescendant thereof, that has been altered in such a way that higherlevels of such protein are expressed than normal, compared to theunaltered host cell. Thus, included within this category are expressionof proteins foreign to the host cell, proteins not naturally expressedby the host cell, or proteins naturally expressed by the host cell atrelatively low levels that increase after alteration of the host cell.

The section headings are used herein for organizational purposes only,and are not to be construed as in any way limiting the subject matterdescribed.

Increasing Alpha 1,2-Mannosidase (MAN1C1) Activity

The invention contemplates that increasing the levels of alpha1,2-mannosidase (MAN1C1) activity in host cells during production of aprotein of interest may be accomplished through any means known in theart, including by adding a chemical inducer or through overexpression ofMAN1C1 enzyme. The MAN1C1 enzyme that the host cell overexpresses mayhave the same or similar sequence as a MAN1C1 that is endogenous, ornative, to the host cell. Thus, human MAN1C1 may be overexpressed inhuman host cells, CHO MAN1C1 may be overexpressed in CHO host cells, andsimilarly native enzyme that carries out the MAN1C1 function may beoverexpressed in other host cells. However, any MAN1C1 enzyme thatfunctions in the same way in the desired host cell may be used,including an ortholog, or a biologically active fragment, variant,analog or derivative.

As used herein, “analog” refers to a nucleotide or amino acid sequencethat has insertions, deletions or substitutions relative to the parentsequence, while still substantially maintaining the biological activityof the parent sequence, as determined using biological assays known toone of skill in the art. “Variants” include naturally occurring allelicvariants, splice variants, or polymorphic forms of the parent sequence.“Derivatives” of naturally occurring, variant or analog polypeptidesinclude those which have been chemically modified, for example, toattach water soluble polymers (e.g., polyethylene glycol),radionuclides, or other diagnostic or targeting or therapeutic moieties,any of which can be attached directly or indirectly through linkers.

“Biologically active” with respect to a MAN1C1 polypeptide means thatthe fragment, variant, derivative or analog thereof retains similaractivity in improving specific productivity, e.g. as measured as amountof protein of interest produced per cell per day, or retains similarenzymatic activity in removing mannose from a suitablemannose-containing substrate. “Biologically active” with respect to aMAN1C1 nucleic acid means that the nucleic acid encodes such abiologically active MAN1C1 polypeptide.

The nucleotide and amino acid sequences of an exemplary human MAN1C1 areset forth in SEQ ID NOS: 1 and 2, respectively. Nucleotides 331 through2223 of the polynucleotide of SEQ ID NO: 1 encode the MAN1C1 polypeptideof SEQ ID NO: 2. The nucleotide and polypeptide sequences for humanMAN1C1 (SEQ ID NOS: 1 and 2, respectively, were identified by Tremblayet al. (J. Biol. Chem. 275: 31655-31660, 2000) and are provided inGenbank Accession No. AF261655. Exemplary polynucleotide and polypeptidesequences of other orthologs and variants of MAN1C1 are identified inGenbank Accession Nos. AB209275 (SEQ ID NOS: 12 and 13) and DV567987(SEQ ID NO: 14).

The term “MAN1C1” as used herein refers to human MAN1C1 (the polypeptideof SEQ ID NO: 2 encoded by the polynucleotide of SEQ. ID NO: 1),orthologs thereof, or a biologically active fragment, variant, analog,or derivative of the human enzyme or orthologs. Exemplary analogs retain65% or higher amino acid identity to the parent sequence, or 70%, 75%,80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% or higheridentity. Exemplary fragments include fragments of at least 25, 50, 75,100, or more amino acid residues of a MAN1C1 polypeptide. Otherexemplary MAN1C1 fragments, variants, analogs or derivatives includethose encoded by nucleic acids that would hybridize under highly ormoderately stringent conditions to the nucleotide sequence of SEQ ID NO:1 or any other orthologs of the nucleotide sequence of SEQ ID NO: 1.

As used herein, the term “MAN1C1 nucleic acid” or “MAN1C1polynucleotide” refers to a nucleic acid that encodes any of thepreceeding polypeptides, including a nucleotide sequence as set forth inSEQ ID NO: 1, or nucleic acids comprising nucleotide sequences that areat least about 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99% or100% identical thereto, or nucleic acids which hybridize undermoderately or highly stringent conditions as defined herein with thecomplement of SEQ ID NO: 1 or any other orthologs of the nucleotidesequence of SEQ ID NO: 1.

It is also understood that MAN1C1 nucleic acids include allelic orsplice variants of a MAN1C1 nucleic acid of SEQ ID NO: 1 or any otherorthologs, and include nucleotide sequences which are complementary toany of the above nucleotide sequences.

Where a gene encoding a MAN1C1 polypeptide has been identified from onespecies, all or a portion of that gene may be used as a probe or primerto identify corresponding genes from other species (orthologs, or“species homologs”) or related genes from the same species (homologs).The probes or primers may be used for hybridization screening or PCRamplification of genomic DNA or cDNA libraries from various tissuesources believed to express the MAN1C1 gene. Appropriate conditions ofhybridization stringency can be determined by one of ordinary skill inthe art. Bioinformatic techniques can also be used to identifyorthologs, wherein collections of sequences from various mammalian orother species are screened for nucleotide or polypeptide sequences thatexhibit significant homology to known MAN1C1 sequences. Nucleic acidsencoding MAN1C1 polypeptides may also be identified by expressioncloning which employs the detection of positive clones based upon aproperty of the expressed protein. Typically, nucleic acid libraries arescreened by the binding of an antibody or other binding partner (e.g.,receptor or ligand) to cloned proteins which are expressed and displayedon a host cell surface. The antibody or binding partner is modified witha detectable label to identify those cells expressing the desired clone.

Although the invention primarily contemplates that MAN1C1 will beoverexpressed, i.e., expressed in the altered host cell at a greaterlevel than normal in the unaltered host cell, the invention alsocontemplates methods for decreasing or inhibiting the expression ofMAN1C1 in cells, e.g. through administration of siRNA or antisensecompounds.

Inducers of Protein Production

The invention also contemplates the use of other known inducers ofprotein production in combination with the host cells which overexpressMAN1C1 and another protein of interest, to further increase overallproduction of the protein of interest. Known inducers include, but arenot limited to, the following compounds: N-Acetyl-L-cysteine,Actinomycin D, 7-Amino-, Bafilamycin A1, Streptomyces griseus,Calphostin C, Cladosporium cladosporioides, Camptothecin, Camptothecaacuminata, CAPE, 2-Chloro-2′-deoxyadenosine, 2-Chloro-2′-deoxyadenosine5′-Triphosphate, Tetralithium Salt, Cycloheximide, CyclophosphamideMonohydrate, Cyclosporine, Trichoderma polysporum, Daunorubicin,Hydrochloride, Dexamethasone, Doxorubicin, Hydrochloride,(−)-Epigallocatechin Gallate, Etoposide, Etoposide Phosphate,ET-18-OCH3, 5-Fluorouracil, H-7, Dihydrochloride, Genistein,4-Hydroxynonenal, 4-Hydroxyphenylretinamide, Hydroxyurea, IL-1βInhibitor, (±)-S-Nitroso-N-acetylpenicillamine, S-Nitrosoglutathione,Phorbol-12-myristate-13-acetate, Puromycin, Dihydrochloride,1-Pyrrolidinecarbodithioic Acid, Ammonium Salt, Quercetin, Dihydrate,Rapamycin, Sodium Butyrate, Sodium 4-Phenylbutyrate,D-erythro-Sphingosine, N-Acetyl-, D-erythro-Sphingosine, N-Octanoyl-,Staurosporine, Streptomyces sp., Sulindac, Thapsigargin, TRAIL, E. coli,Trichostatin A, Streptomyces sp., (±)-Verapamil, Hydrochloride,Veratridine, Vitamin D3, 1α, 25-Dihydroxy-, and Vitamin E Succinate (VWRand Calbiochem).

The invention further contemplates the identification of other chemicalsthat improve protein production through increasing MAN1C1 activity, forexample via increasing MAN1C1 expression. Increases in MAN1C1 activitycan be determined as described by Tremblay et al. (2000, supra).

Increases in MAN1C1 expression can be determined by measuring relativeamounts of MAN1C1 mRNA produced as described in Example 4 (usingAffymetrix chip) or Example 5 (quantitative PCR), or MAN1C1 proteinproduced via ELISA, HPLC, or other methods known in the art or asdescribed by Tremblay et al. (2000, supra).

Proteins of Interest for Recombinant Production

The recombinant protein of interest that the host cell overexpresses canbe any polypeptide, either endogenous (native) or exogenous to the cell.Exemplary proteins of interest are glycoproteins, including secretedglycoproteins. In exemplary embodiments, the glycoprotein of interest isan erythropoiesis-stimulating molecule, described below.

The amount of recombinant protein of interest produced may be measuredas “specific productivity,” which is the amount of protein of interestproduced per cell per day. The amount of recombinant protein of interestproduced may also be measured by amount of protein of interest producedper amount of cell protein. Methods of measuring specific productivityor protein production are well known in the art.

The recombinant proteins of interest for which expression can beincreased using the materials and methods of the invention can be anypolypeptide, either endogenous or exogenous to the cell. Exemplaryrecombinant proteins of interest are glycoproteins, especiallyN-glycosylated glycoproteins. Exemplary glycoproteins of interestinclude secreted glycoproteins such as erythropoiesis-stimulatingmolecules.

The terms “polypeptide” and “protein” are used interchangeably herein.

The term “erythropoiesis-stimulating molecules” as used herein includeshuman erythropoietin (SEQ. ID NO.: 3) or a biologically active variant,derivative, or analog thereof, including a chemically modifiedderivative of such protein or analog. Amino acids 1 through 165 of SEQID NO: 3 constitute the mature protein. Another exemplaryerythropoiesis-stimulating molecule is darbepoetin (SEQ ID NO: 5). Aminoacids 1 through 165 of SEQ. ID NO: 5 constitute the mature protein. Alsocontemplated are analogs of erythropoietin (SEQ ID NO: 3) or darbepoetin(SEQ. ID NO: 5), with 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%,95%, 96%, 97%, 98%, or 99% identity to SEQ. ID NO: 3 or SEQ. ID NO: 5,respectively, and still retaining erythropoietic activity.

Exemplary sequences, manufacture, purification and use of recombinanthuman erythropoietin are described in a number of patent publications,including but not limited to Lin U.S. Pat. No. 4,703,008 and Lai et al.U. S. Pat. No. 4,667,016, each of which is incorporated herein byreference in its entirety. Darbepoetin is a hyperglycosylatederythropoietin analog having five changes in the amino acid sequence ofrHuEPO which provide for two additional carbohydrate chains. Morespecifically, darbepoetin contains two additional N-linked carbohydratechains at amino acid residues 30 and 88 of SEQ ID NO: 5. Exemplarysequences, manufacture, purification and use of darbepoetin and othererythropoietin analogs are described in a number of patent publications,including Strickland et al., 91/05867, Elliott et al., WO 95/05465,Egrie et al., WO 00/24893, and Egrie et al. WO 01/81405, each of whichis incorporated herein by reference in its entirety. Derivatives ofnaturally occurring or analog polypeptides include those which have beenchemically modified, for example, to attach water soluble polymers(e.g., pegylated), radionuclides, or other diagnostic or targeting ortherapeutic moieties.

The term “erythropoietic activity” means activity to stimulateerythropoiesis as demonstrated in an in vivo assay, for example, theexhypoxic polycythermic mouse assay. See, e.g., Cotes and Bangham,Nature 191:1065 (1961).

Other polypeptides of interest for which recombinant production can beincreased using the materials and methods of the invention includecytokines, immunoglobulin-like proteins, antibodies, and peptibodies,and analogs, variants, or derivatives of any of these proteins.

Exemplary proteins of interest include granulocyte-colony stimulatingfactor (GCSF), stem cell factor, leptin, hormones, cytokines,hematopoietic factors, growth factors, antiobesity factors, trophicfactors, anti-inflammatory factors, receptors or soluble receptors, suchas a soluble fragment of p80 TNF-R, enzymes, and Fc-fusions of any ofthe preceding. Other examples include insulin, gastrin, prolactin,adrenocorticotropic hormone (ACTH), thyroid stimulating hormone (TSH),luteinizing hormone (LH), follicle stimulating hormone (FSH), humanchorionic gonadotropin (HCG), motilin, interferons (alpha, beta, gamma),interleukins (IL-1 to IL-12), tumor necrosis factor (TNF), tumornecrosis factor-binding protein (TNF-bp) or TNF receptor-I or -II, brainderived neurotrophic factor (BDNF), glial derived neurotrophic factor(GDNF), neurotrophic factor 3 (NT3), fibroblast growth factors (FGF),neurotrophic growth factor (NGF), bone growth factors such asosteoprotegerin (OPG), insulin-like growth factors (IGFs), macrophagecolony stimulating factor (M-CSF), granulocyte macrophage colonystimulating factor (GM-CSF), megakaryocyte derived growth factor (MGDF),keratinocyte growth factor (KGF), thrombopoietin, platelet-derivedgrowth factor (PGDF), colony simulating growth factors (CSFs), bonemorphogenetic protein (BMP), superoxide dismutase (SOD), tissueplasminogen activator (TPA), urokinase, streptokinase, or kallikrein,receptors or soluble receptors, enzymes, variants, derivatives, oranalogs including Fc-fusions of any of these proteins.

As used herein, the term “antibody” includes fully assembled antibodies,monoclonal antibodies (including human, humanized or chimericantibodies), polyclonal antibodies, multispecific antibodies (e.g.,bispecific antibodies), Maxibody, and antibody fragments that can bindantigen (e.g., Fab′, F′(ab)2, Fv, single chain antibodies, diabodies),comprising complementarity determining regions (CDRs) of the foregoingas long as they exhibit the desired biological activity.

Exemplary antibodies are Herceptin® (Trastuzumab), a recombinantDNA-derived humanized monoclonal antibody that selectively binds to theextracellular domain of the human epidermal growth factor receptor 2(Her2) proto-oncogene; and Rituxan® (Rituximab), a geneticallyengineered chimeric murine/human monoclonal antibody directed againstthe CD20 antigen found on the surface of normal and malignant Blymphocytes. Other exemplary antibodies include Avastin® (bevacizumab),Bexxar® (Tositumomab), Campath® (Alemtuzumab), Erbitux® (Cetuximab),Humira® (Adalimumab), Raptiva® (efalizumab), Remicade® (Infliximab),ReoPro® (Abciximab), Simulect® (Basiliximab), Synagis® (Palivizumab),Xolair® (Omalizumab), Zenapax® (Daclizumab), Zevalin® (IbritumomabTiuxetan ), or Mylotarg® (gemtuzumab ozogamicin), receptors or solublereceptors, enzymes, variants, derivatives, or analogs of any of theseantibodies.

Peptibodies, molecules comprising an antibody Fc domain attached to atleast one antigen-binding peptide, are generally described in PCTpublication WO 00/24782, published May 4, 2000. Immunoglobulin-likeproteins, members of the immunoglobulin superfamily, contain one or Moreimniunoglobulin-like domains which fold in structures similar toportions of tle antibody variable region.

Engineering Host Cells to Overexpress Protein

Host cells can be engineered to overexpress a protein in a variety ofways known in the art, including but not limited to insertion ofexogenous nucleic acid encoding the desired protein, optionally as partof an expression vector, insertion of an exogenous expression controlsequence such that it causes increased expression of the host cell'sendogenous gene encoding the desired protein, or activation of the hostcell's eridogenous expression control sequence(s) to increase expressionof endogenous gene encoding the desired protein.

Cultures of host cells can be prepared according to any methods known inthe art, and methods of growing such host cells and recoveringrecombinant protein produced by the cells, whether from the cells orculture medium, are known in the art. Such culturing methods may involveaddition of chemical inducers of protein production to the culturemedium. Exemplary host cells and procedures are described below.

A nucleic acid encoding a MAN1C1 polypeptide may be inserted into anappropriate expression vector using standard ligation techniques.Expression vectors optionally may include a promoter, one or moreenhancer sequences, an origin of replication, a transcriptionaltermination sequence, a complete intron sequence containing a donor andacceptor splice site, a sequence encoding a leader or signal sequencefor polypeptide secretion, a ribosome binding site, a polyadenylationsequence, a polylinker region for inserting the nucleic acid encodingthe polypeptide to be expressed, and/or a selectable marker element.Each of these sequences is discussed below.

Optionally, the vector may contain a “tag”-encoding sequence, i.e., anoligonucleotide sequence located at the 5′ or 3′ end of the MAN1C1polypeptide coding sequence; the oligonucleotide molecule encodespolyHis (such as hexaHis), or another “tag” such as FLAG, HA(hemaglutinin influenza virus) or myc for which commercially availableantibodies exist. This tag is typically fused to the polypeptide uponexpression of the polypeptide, and can serve as a means for detection oraffinity purification of the MAN1C1 polypeptide from the host cell.

Suitable vectors include, but are not limited to, cosmids, plasmids, ormodified viruses, but it will be appreciated that the vector system mustbe compatible with the selected host cell. Nucleic acid can betransferred into host cells by any means known in the art, e.g. throughliposome-mediated transfer, receptor-mediated transfer (ligand-DNAcomplex), electroporation, microinjection of DNA, cell fusion,DEAE-dextran, calcium chloride, calcium phosphate precipitation,microparticle bombardment, infection with viral vectors, lipofection,transfection, or homologous recombination.

The invention also contemplates use of homologous recombination or otherrecombinant production methods utilizing control elements introducedinto cells already containing DNA encoding MAN1C1 polypeptides. Forexample, homologous recombination methods may be used to modify a cellthat contains a normally transcriptionally silent MAN1C1 gene, or anunder expressed gene, and thereby produce a cell which expressestherapeutically efficacious amounts of MAN1C1 polypeptides. Homologousrecombination is a technique originally developed for targeting genes toinduce or correct mutations in transcriptionally active genes(Kucherlapati, Prog. Nucl. Acid Res. & Mol. Biol. 36: 301, 1989). Thebasic technique was developed as a method for introducing specificmutations into specific regions of the mammalian genome (Thomas et al.,Cell 44: 419-428, 1986; Thomas et al., Cell 51:503-512, 1987; Doetschmanet al., Proc. Natl. Acad. Sci. 85: 8583-8587, 1988) or to correctspecific mutations within defective genes (Doetschman et al., Nature330: 576-578, 1987). Exemplary homologous recombination techniques aredescribed in U.S. Pat. No. 5,272,071 (EP 9193051, EP Publication No.505500; PCT/US90/07642, International Publication No. WO 91/09955).

Through homologous recombination, the DNA sequence to be inserted intothe genome can be directed to a specific region of the gene of interestby attaching it to targeting DNA. The targeting DNA is a nucleotidesequence that is complementary (homologous) to a region of the genomicDNA. Small pieces of targeting DNA that are complementary to a specificregion of the genome are put in contact with the parental strand duringthe DNA replication process. It is a general property of DNA that hasbeen inserted into a cell to hybridize, and therefore, recombine withother pieces of endogenous DNA through shared homologous regions. Ifthis complementary strand is attached to an oligonucleotide thatcontains a mutation or a different sequence or an additional nucleotide,it too is incorporated into the newly synthesized strand as a result ofthe recombination. As a result of the proofreading function, it ispossible for the new sequence of DNA to serve as the template. Thus, thetransferred DNA is incorporated into the genome.

Attached to these pieces of targeting DNA are regions of DNA which mayinteract with or control the expression of a MAN1C1 polypeptide, e.g.,flanking sequences. For example, a promoter and/or enhancer element, oran exogenous transcription modulatory element, optionally including anintron, is inserted in the genome of the intended host cell in proximityand orientation sufficient to influence the transcription of DNAencoding the desired MAN1C1 polypeptide. The control element controls aportion of the DNA present in the host cell genome. Thus, the expressionof MAN1C1 polypeptide may be achieved not by transfection of DNA thatencodes the MAN1C1 gene itself, but rather by the use of targeting DNA(containing regions of homology with the endogenous gene of interest)coupled with DNA regulatory segments that provide the endogenous genesequence with recognizable signals for transcription of a MAN1C1polypeptide.

In an exemplary embodiment, DNA which includes at least a regulatorysequence, an exon and a splice donor site is introduced into thechromosomal DNA in such a manner as to produce a new transcription unit(in which the regulatory sequence, the exon and the splice donor sitepresent in the DNA construct are operatively linked to the endogenousgene).

Overexpression, as described herein, encompasses activating (or causingto be expressed) a gene which is normally silent (unexpressed) in thecell as obtained, as well as increasing the expression of a gene whichis not expressed at physiologically significant levels in the cell asobtained.

Site-specific recombination systems such as Cre/loxP, FLP/FRT are knownin the art (Sauer, Curr. Opin. Biotechnol. 521-527, 1994; Sauer, Meth.Enzymol. 225: 890-900, 1993).

An additional approach for increasing, or causing, the expression ofMAN1C1 polypeptide from a cell's endogenous MAN1C1 gene involvesincreasing the expression of transcription factors that upregulateexpression of the gene and/or decreasing the expression oftranscriptional repressors that downregulate expression of the gene, ina manner which results in de novo or increased MAN1C1 polypeptideproduction from the cell's endogenous MAN1C1 gene.

Thus, the invention contemplates host cells into which nucleic acidencoding MAN1C1 has been inserted, optionally operably linked to anexpression control sequence, and optionally as part of an expressionvector. The invention also contemplates host cells into which aheterologous expression control sequence has been inserted in such amanner as to increase MAN1C1 expression, including host cells in whichthe native MAN1C1 gene is operably linked to a heterologous expressioncontrol sequence.

Any host cells or hosts known in the art for recombinant proteinproduction may be used, including yeast cells, plant cells, plants,insect cells, and mammalian cells, and transgenic animals. Exemplaryyeast cells include Pichia, e.g. P. pastoris, and Saccharomyces e.g. S.cerevisiae, as well as Schizosaccharomyces pombe, Kluyveromyces, K.Zactis, K. fragilis, K. bulgaricus, K. wickeramii, K. waltii, K.drosophilarum, K. thernotolerans, and K. marxianus; K. yarrowia;Trichoderma reesia, Neurospora crassa, Schwanniomyces, Schwanniomycesoccidentalis, Neurospora, Penicillium, Totypocladium, Aspergillus, A.nidulans, A. niger, Hansenula, Candida, Kloeckera, Torulopsis, andRhodotorula. Exemplary insect cells include Autographa californica andSpodoptera frugiperda, and Drosophila. Exemplary mammmalian cellsinclude varieties of CHO, BHK, HEK-293, NS0, YB2/3, SP2/0, and humancells such as PER-C6 or HT1080, as well as VERO, HeLa, COS, MDCK,NIH3T3, Jurkat, Saos, PC-12, HCT 116, L929, Ltk-, WI38, CV1, TM4, W138,Hep G2, MMT, a leukemic cell line, embryonic stem cell or fertilized eggcell.

Culturing Methods and Polypeptide Production

The invention also provides methods for culturing, i.e. growing, hostcells under conditions that increase MAN1C1 protein expression andresult in increased specific productivity or protein production of anyof the recombinant proteins of interest described herein. Such methodsmay further include the step of recovering the recombinant protein ofinterest produced from the host cells or culture medium.

When the recombinant protein of interest is secreted into the medium,the medium can be harvested periodically, so that the same host cellscan be used through several harvest cycles. In exemplary embodiments,host cells producing erythropoiesis-stimulating molecules are incubatedin three discrete batch harvest cycles. For each cycle, medium isharvested and replaced with fresh medium replacing the harvested medium.The first cycle may be, e.g., 8 days; the second cycle, e.g., 7 days;and the third cycle, e.g., 5 days in duration.

A variety of culture systems are known in the art, including T-flasks,spinner and shaker flasks, roller bottles and stirred-tank bioreactors.Roller bottle cultivation is generally carried out by seeding cells intoroller bottles that are partially filled (e.g., to 10-30% of capacity)with medium and slowly rotated, allowing cells to attach to the sides ofthe bottles and grow to confluency. The cell medium is harvested bydecanting the supernatant, which is replaced with fresh medium.Anchorage-dependent cells can also be cultivated on microcarrier, e.g.polymeric spheres, that are maintained in suspension in stirred-tankbioreactors. Alternatively, cells can be grown in single-cellsuspension.

Culture medium may be added in a batch process, e.g. where culturemedium is added once to the cells in a single batch, or in a fed batchprocess in which small batches of culture medium are periodically added.Medium can be harvested at the end of culture or several times duringculture. Continuously perfused production processes are also known inthe art, and involve continuous feeding of fresh medium into theculture, while the same volume is continuously withdrawn from thereactor. Perfused cultures generally achieve higher cell densities thanbatch cultures and can be maintained for weeks. or months with repeatedharvests.

Host cells of the invention may be cultured using standard media wellknown to the skilled artisan. The media will usually contain allnutrients necessary for the growth and survival of the cells. Suitablemedia for culturing eukaryotic cells are, Roswell Park MemorialInstitute medium 1640 (RPMI 1640), Minimal Essential Medium (MEM),and/or Dulbecco's Modified Eagle Medium (DMEM), all of which may besupplemented with serum and/or growth factors as indicated by theparticular cell line being cultured. A suitable medium for insectcultures is Grace's medium supplemented with yeastolate, lactalbuminhydrolysate, and/or fetal calf serum as necessary.

Typically, an antibiotic or other compound useful for selective growthof transformed cells is added as a supplement to the media. The compoundto be used will be dictated by the selectable marker element present onthe plasmid with which the host cell was transformed. For example, wherethe selectable marker element is kanamycin resistance, the compoundadded to the culture medium will be kanamycin. Other compounds forselective growth include ampicillin, tetracycline, geneticin, andneomycin.

The amount of a MAN1C1 polypeptide and the amount of desired recombinantprotein of interest produced by a host cell can be evaluated usingstandard methods known in the art. Such methods include, withoutlimitation, Western blot analysis, SDS-polyacrylamide gelelectrophoresis, non-denaturing gel electrophoresis, High PerformanceLiquid Chromatography (HPLC) separation, immunoprecipitation, and/oractivity assays such as DNA binding gel shift assays. The invention alsocontemplates that specific productivity (expressed as pg/cell/day) ofprotein of interest can be evaluated using standard methods as known inthe art and as described herein.

EXAMPLES

The present invention is described in more detail with reference to thefollowing non-limiting examples, which are offered to more fullyillustrate the invention, but are not to be construed as limiting thescope thereof. The examples illustrate various methods used in theinvention, such as cell culture methods; recombinant HuEPO quantitationby RP-HPLC; analysis of gene expression using Affymetrix chips;quantitative real time PCR of selected genes; the use of MAN1C1 siRNA;and MAN1C1 cloning and expression. The examples also illustrate theeffect of sodium butyrate on rHuEPO specific productivity and cell cycleprogression; the effect of sodium butyrate on MAN1C1 expression; theeffect of MAN1C1 small interfering RNA (siRNA) on rHuEPO specificproductivity; and the effect of the overexpression of MAN1C1 on rHuEPOspecific productivity.

The techniques described in these examples represent techniquesdescribed by the inventors to function well in the practice of theinvention, and as such constitute exemplary modes for the practicethereof. Many changes can be made in the specific methods that aredisclosed and still obtain a like or similar result without departingfrom the spirit and scope of the invention. Such variations are intendedas aspects of the invention.

Example 1 Cell Culture Methods

A human kidney fibrosarcoma cell line, HT1080 (Rasheed et al., Cancer33: 1027-1033, 1974), transfected with a plasmid for human EPO cDNA wasused throughout the experiments described in the Examples as set outbelow. Selective pressure for the retention of the transfected plasmidwas maintained with the antibiotic geneticin (Gibco). Cells were grownas attached monolayers in vented T-flasks (75 cm²) (Corning) at aninoculation density of 2.1×10⁴ cells/cm² in a humidified 12% CO₂incubator at 37° C. Cells were grown for 4-5 days. in 10% serumcontaining DMEM media supplemented with 1× Non-Essential amino acids, 5mg/L geneticin, and 1.5 g/L sodium bicarbonate (all from Gibco). Aftercells reached confluence, they were washed with PBS to remove the serumand switched to serum-free 1:1 DMEM/F-12 media supplemented with 1×Non-Essential amino acids (Gibco), 1.5 g/L sodium bicarbonate, and 2 g/Lglucose for a period of 5 to 7 days. Experimental cultures were treatedwith 2 mM sodium butyrate (Sigma) on the same day as the serum-freemedia addition.

Example 2 Recombinant HuEPO Quantitation by RP-HPLC

To determine the amount of recombinant human erythropoietin (rHuEPO)produced in cell culture media, 200 μl of media were analyzed byreversed phase HPLC. Samples were separated on an analyticalstyrene/divinylbenzene HPLC column equipped with a guard column (PolymerLabs) using a linear gradient from 30-65% CH₃CN in 0.1% TFA over 17minutes (Sigma). The retention time for rHuEPO expressed in cell culturewas approximately 15.5 minutes and corresponded with a purified rHuEPOstandard (Amgen Inc). Integrated peak areas of unknown samples werequantitated by comparison to a standard curve of purified rHuEPO.

Example 3 Analysis of Gene Expression Using Affymetrix Chip

The expression of genes in HT1080 cells was studied over a 24 hourperiod in the presence and absence of sodium butyrate usingoligonucleotide microarrays and the HU133A Affymetrix chip (Affymetrix).All experiments were carried out according to Affymetrix protocols. Atotal of 24 chips were analyzed—12 from sodium butyrate-treated cellsand 12 controls. The gene expression data from the Affymetrix softwarewas first imported into GeneSpring® version 6.0 and normalized using thesoftware's global normalization procedure. Values below 0.01 were set to0.01 and each measurement was divided by the 50^(th) percentile of allmeasurements for that sample. Each gene was then divided by the medianof its measurements in all samples, and if the median of the raw valueswas below 10, then each measurement for that gene was divided by 10.Sample data for each chip was then grouped by treatment type (control orsodium butyrate) and by time (3, 6, 12, and 24 hours). Results from theexpression data were compared to the publicly available gene list fromthe Consortium for functional Glycomics cDNA array (GLYCOv2 Gene Chip)for genes present in four categories: glycan degradation, glycantransferase, glycan transport, and sugar nucleotides, as defined by theConsortium gene list.

Example 4 Quantitative Real Time PCR of Selected Genes

TaqMan (Applied Biosystems Inc.) reverse transcription quantitative realtime PCR (qRT-PCR) was used to verify the changes in mRNA expressionseen.using the Affymetrix chip. Probes to MAN1C1 and rHuEPO weregenerated using Primer Express software (Applied BiosystemsIncorporated). MAN1C1: Forward- GGA GCC CCA GAG CCA AGT (SEQ ID NO: 6);Reverse- GCC AAG CAA ACT GCA TCA TCT (SEQ ID NO: 7); TaqMan- ECG AGC CCAGCG GGA GAA AAT CAX (E=6-FAM; X=Tamra) (SEQ ID NO: 8). rHuEPO: Forward-GTT AAT TTC TAT GCC TGG AAG AGG AT (SEQ ID NO: 9); Reverse- CCA GGC CCTGCC AGA CTT (SEQ ID NO: 10); TaqMan- EAG GTC GGG CAG CAG GCC GTX(E=6-FAM; X=Tamra) (SEQ ID NO: 11). An ABI 7000 or 7900 (AppliedBiosystems Inc.) was used for each analysis with the following thermalcycling parameters; 1 cycle at 50° C. for 30 min; 1 cycle at 95° C. for10min; 40. cycles at 94° C. for 15 sec and 60° C. for 60 sec. RNAsamples from at least three independent cell cultures were assayed intriplicate for both control and sodium butyrate-treated cells. The cyclethreshold (Ct) values for all genes tested were normalized to thehousekeeping gene, GAPDH (Applied Biosystems Inc., part #4310884E), tocorrect for error in RNA concentrations. Data was reported as either“fold change” or “percent change” in Ct levels for sodium butyratetreated samples as compared to control samples.

Example 5 MAN1C1 siRNA

HT1080 cells were grown in 75 cm² vented T-flasks for 4 days in 10%serum containing DMEM media supplemented with 1× Non-Essential aminoacids, and 1.5 g/L sodium bicarbonate (all from Gibco). After cellsreached confluence they were washed 1× with PBS and then treated with orwithout 50 μL siPOR™ Amine transfection agent plus 60 μM of smallinhibitory RNA (siRNA) (Ambion) in 15 mL of 10% serum containing DMEMmedia for a period of 48 hours. Cultures were then washed with PBS toremove serum and switched into 15 mL serum free DMEM:F12 media with orwithout 50 μL siPORT™ Amine and 60 uM siRNA. Cultures were then grownfor a period of 5 days in the presence and absence of 2 mM sodiumbutyrate. Samples of media were collected and rHuEPO and mRNA levelswere assayed on Days 1, 3, and 5 post serum-free shift.

Example 6 MAN1C1 Cloning and Expression

A _(p)ENTR™ 221 entry vector containing the cDNA sequence of MAN1C1 (SEQID NO: 1) and flanking attL recombination sites was used(Invitrogen—clone ID:IOH42767). Following the gateway technologyprocedure, recombination, using LR Clonase™ of the entry clone two attLsites with the destination pcDNA3.1/nV5-DEST™ vector two attR sites, wasperformed and verified by transformation of DH5α competent cells underampicillin selection. (The destination vector contains the ccdB genethat allows for negative selection in the recombination reaction.)Restriction enzyme digestion of the destination vector afterrecombination and transformation with BamHI confirmed the properrecombination reaction (data not shown). A plasmid preparation of DNA(˜3 mg) was obtained using the manufacturer's protocol for the Giga PrepPlasmid DNA Kit (Qiagen).

Transfection of HT1080 cells was performed as follows: T-flasks (75 cm²)were inoculated at 1.6×10⁶ cells and allowed to grow for 4 to 5 daysprior to transfection. Either 16, 32, or 64 μg of plasmid DNA was addedto 2 mL of DMEM:F12 media. In addition, 59 μL Lipofectamine 2000(Invitrogen) was added to a separate 2 mL of DMEM:F12 media andincubated for 5 minutes. The two mixtures of DNA and Lipofectamine werethen combined and allowed to incubate for 20 minutes at roomtemperature. Following a 1× PBS wash of the T-flasks, the entire mixture(˜4 mL) was added and allowed to incubate for 2 hours in a 37° C./12%CO₂ incubator. An additional 11 mL of fresh DMEM:F12 media was added toeach T-flask, and sampling began 24 hours later.

Example 7 Sodium Butyrate Increases rHuEPO Specific Productivity andBlocks Cell Cycle Progression

The effect that sodium butyrate treatment has on the HT1080 cell cycleand rHuEPO specific productivity was examined. Cells treated with sodiumbutyrate (2 mM) increased recombinant human erythropoietin (rHuEPO)specific productivity roughly four-fold compared to control cultures(FIG. 1). However, instead of sodium butyrate shifting the cells intothe G0/G1 phase, where other investigators have reported proteinsynthesis is maximized (Kim et al., Biotech. Bioeng. 71: 184, 2001), thepopulation of cells in G0/G1, S, and G2/M-phases remained relativelyconstant over the entire 5 days of culture as compared to controlcultures. These differences may be due to the culturing methods as setout above, which allowed the cells to reach confluence prior to theaddition of sodium butyrate, whereas previous reports looked at cellcycle effects on exponentially growing cells at the time of sodiumbutyrate addition. Therefore, cell cycle data alone cannot beresponsible for the increases in rHuEPO specific productivity that weremeasured.

Example 8 Sodium Butyrate Increases MAN1C1 Expression

Recombinant HuEPO, produced in HT1080 cultures, was used as a modelglycoprotein to study the effects of sodium butyrate on genes involvedin protein glycosylation. Treatment of HT1080 cells with 2 mM sodiumbutyrate in culture resulted in numerous phenotypic changes with respectto sugar nucleotide pools and the oligosaccharide structures present onrHuEPO.

To determine if these phenotypic changes were associated with geneticchanges, the expression of genes in HT1080 cells was studied over a 24hour period in the presence and absence of sodium butyrate usingoligonucleotide microarrays and the HU133A Affymetrix chip (Affymetrix).

A potential rate-limiting enzyme, alpha 1,2 mannosidase I enzyme(MAN1C1), involved in glycoprotein N-linked oligosaccharide processing,was identified. The relative change in MAN1C1 mRNA induced by sodiumbutyrate is set forth below in Table 1. This gene increase in expressionroughly 10-fold over the course of twenty-four hours when cells weretreated with sodium butyrate (Table 1). Subsequent validation of theMAN1C1 expression by qRT-PCR for HT1080 cells treated with sodiumbutyrate over a five day period showed increases >40-fold as compared tocontrol cultures (Table 1). TABLE 1 Summary of qRT-PCR Data for HT1080MAN1C1 mRNA Fold Change Time Point (hr)^(A) Fold Change^(B) StandardDeviation 3 8.7 ±2.1 6 38.7 ±9.5 12 36.0 ±4.6 24 53.3 ±14.4 72 42.2 ±3.8120 7.8 ±3.6^(A)Time after sodium butyrate added to culture^(B)Fold change as compared to untreated HT1080 cells

Example 9 MAN1C1 Small Interfering RNA (siRNA) Reduces rHuEPO SpecificProductivity

To determine if a link existed between sodium butyrate's effect onincreases in MAN1C1 expression and increases in rHuEPO specificproductivity, cells were treated with small interfering RNA (siRNA)against MAN1C1 in the presence and absence of sodium butyrate. Treatmentwith siRNA had no impact on rHuEPO Q_(P) under control conditions, butdecreased rHuEPO Q_(P) 50% when cells were treated with both sodiumbutyrate and the siRNA as compared to sodium butyrate alone (FIG. 2A).As previously shown, sodium butyrate treatment increases MAN1C1 mRNAlevels as compared to control cultures (FIG. 2B), however, cells treatedwith both sodium butyrate and siRNA had an ˜30% decrease in MAN1C1 mRNAlevels as compared to cells treated with sodium butyrate alone (FIG.2B). It should be noted that MAN1C1 mRNA levels were still higher in thesodium butyrate and siRNA treated cells as compared to controls (FIG.2B). This correlated to a rHuEPO Q_(P) that remained higher than controlin both cells treated with sodium butyrate alone and cells treated withsodium butyrate and siRNA, although the absolute levels of Q_(P) werereduced (FIG. 2A).

To ensure that changes in specific productivity measurements were notcaused by a decrease in rHuEPO mRNA levels due to off target effects ofthe siRNA treatment, rHuEPO mRNA levels were measured over the samefive-day period. As shown in FIG. 3, rHuEPO mRNA levels were consistenton day 1 and day 5 in cells treated with sodium butyrate (+/−) siRNA,and were slightly higher on day 5 as compared to control cultures. Thisdata confirms that the siRNA treatment for MAN1C1 did not alter rHuEPOexpression levels by reducing rHuEPO mRNA abundance.

Example 10 Overexpression of MAN1C1 Increases Specific Productivity ofrHuEPO

To confirm that MAN1C1 could account for the increase in rHuEPO Q_(P),independent from sodium butyrate treatment, cells were transfected tooverexpress MAN1C1 under control conditions. As seen in Table 2 (set outbelow), when 16-64 μg of MAN1C1 plasmid DNA was transfected into cells,a large increase (>1000 fold) in MAN1C1 mRNA levels was measured ascompared to un-transfected (control) cells.

The transient expression of MAN1C1 under control conditions (e.g. nosodium butyrate addition) resulted in a 2-3 fold increase in rHuEPOspecific productivity depending on the amount of plasmid DNA transfected(FIG. 4). Although the level of rHuEPO productivity is less than whensodium butyrate alone is used, the data confirms that sodium butyrateincreases MAN1C1 expression, which in turn contributes to the increasein rHuEPO specific productivity. TABLE 2 Summary of % MAN1C1 mRNAincrease after transfection as compared to untransfected cells. % MAN1C1mRNA Increase (n = 2)^(A) Sample Day 1 Day 3 Day 5 16 ug DNA 1683% 1817%2020% 32 ug DNA 1776% 1828% 2149% 64 ug DNA 1650% 1774% 2463%^(A)% increase was calculated by the difference in the cycle at whichabsolute quantitation occurs (Ct—cycle threshold) between cellsuntransfected versus transfected.

All publications, patents and patent applications cited in thisspecification are herein incorporated by reference in their entirety,including but not limited to the material relevant for the reason cited,as if each individual publication or patent application werespecifically and individually indicated to be incorporated by reference.Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity ofunderstanding, it will be readily apparent to those of ordinary skill inthe art in light of the teachings of this invention that certain changesand modifications may be made thereto without departing from the spiritor scope of the appended claims.

1. A host cell engineered to overexpress (a) alpha 1,2 mannosidase(MAN1C1) native to the host cell and (b) a glycoprotein of interest. 2.The host cell of claim 1 wherein said host cell has been transfectedwith a vector comprising a nucleic acid encoding MAN1C1 operably linkedto a heterologous expression control sequence.
 3. The host cell of claim1 wherein said host cell comprises a heterologous expression controlsequence operably linked to a nucleic acid encoding MAN1C1.
 4. The hostcell of any of claims 1-3 wherein said host cell has been transfectedwith a vector comprising a nucleic acid encoding said glycoprotein ofinterest operably linked to a heterologous expression control sequence.5. The host cell of any of claims 1-3 wherein said host cell comprises aheterologous expression control sequence operably linked to a nucleicacid encoding said glycoprotein of interest.
 6. The host cell any ofclaims 1-5 wherein the glycoprotein of interest is anerythropoiesis-stimulating molecule.
 7. The host cell of claim 6 whereinthe glycoprotein of interest is erythropoietin of SEQ ID NO:
 3. 8. Thehost cell of claim 6 wherein the glycoprotein of interest is darbepoetinof SEQ ID NO:
 5. 9. The host cell of any of claims 1-8 which is amammalian cell.
 10. The host cell of any of claims 1-8 which is a CHOcell.
 11. The host cell of any of claims 1-8 which is a human cell. 12.The host cell of any of claims 1-8 which is a BHK cell.
 13. The hostcell of any of claims 1-8 which is an NS/0 cell.
 14. The host cell ofany of claims 1-8 which is an HT-1080 cell.
 15. A method of producing aglycoprotein of interest comprising the steps of: culturing the hostcell of any of claims 1-14 in culture medium; and recovering theglycoprotein of interest from the host cell or culture medium.
 16. Themethod of claim 15 wherein said host is cultured under conditions thatinduce increased MAN1C1 expression.
 17. The method of claim 15 whereinsaid host cell expresses MAN1C1 protein at a level that increasesspecific productivity (pg/cell/day) of glycoprotein of interestproduced.
 18. The method of claim 17 wherein at least a 2-fold increasein specific productivity is achieved by overexpression of MAN1C1.
 19. Amethod of increasing production of a glycoprotein of interest comprisingthe steps of: culturing the host cell of any of claims 1-14 in culturemedium under conditions that permit expression of MAN1C1 at levels thatimprove production of the glycoprotein of interest; and recovering theglycoprotein of interest from the host cell or.culture medium.
 20. Themethod of claim 15 comprising the step of further adding an inducer ofprotein production to the culture medium.
 21. A method of screening foran inducer of protein production comprising the steps of: (a) contactinga host cell with a candidate compound, (b) determining expression levelof MAN1C1, and (c) identifying said candidate compound as an inducer ofprotein production if the expression level of MAN1C1 increases.
 22. Themethod of claim 21 wherein MAN1C1 mRNA expression level is determined.23. The method of claim 21 wherein MAN1C1 protein expression level isdetermined.